1. Field of the Invention
The present invention relates to improved methods for detecting and treating pathological conditions with a multi-step process using compositions containing biotin and/or avidin conjugated to a naturally occurring metal-ion chelating protein.
2. Description of the Prior Art
Antibodies against different determinants associated with pathological and normal cells, as well as associated with pathogenic microorganisms, have been used for the detection and treatment of a wide variety of pathological conditions or lesions. The targeting antibody is conjugated to an appropriate detection or therapeutic agent as described, for example, in Hansen et al., U.S. Pat. Nos. 3,927,193 to Hansen et al., and 4,331.647, 4,348,376, 4,361,544, 4,468,457, 4,444,744, 4,460,459, 4,460,561, 4,624,846 and 4,818,709 to Goldenberg, the disclosure of all of which are incorporated herein by reference.
When detecting a lesion a high signal-to-background ratio needs to be achieved. Therapy also requires a high absolute accretion of the therapeutic agent in the lesion, as well as a reasonably long duration of uptake and binding. High background levels of non-targeting antibody have long been recognized as a major impediment to high target:background ratios being achieved. To overcome this impediment various methods have been developed, such as those described in the above-referenced Goldenberg patents.
Still other methods have been developed to increase the target:background ratios of the detection or therapeutic agents, such as pre-targeting and biotin/avidin approaches, as described, for example, in Goodwin et al., U.S. Pat. No. 4,863,713; Goodwin et al., J. Nucl. Med. 29:226, 1988; Hnatowich et al., J. Nucl. Med. 28:1294, 1987; Oehr et al., J. Nucl. Med. 29:728, 1988; Klibanov et al., J. Nucl. Med. 29:1951, 1988; Sinitsyn et al., J. Nucl. Med. 30:66, 1989; Kalofonos et al., J. Nucl. Med. 31:1791, 1990; Schechter et al., Int. J. Cancer 48:167, 1991; Paganelli et al., Cancer Res. 51:5960, 1991; Paganelli et al., Nucl. Med. Commun. 12:211, 1991; Stickney et al., Cancer Res. 51:6650, 1991; and Yuan et al., Cancer Res. 51:3119, 1991; all incorporated herein in their entirety by reference.
Avidin, found in egg whites, has a very high binding affinity for biotin, which is a B-complex vitamin (Wilcheck et al., Anal. Biochem, 171:1, 1988). Streptavidin, derived from Streptomyces avidinii, is similar to avidin, but has lower non-specific tissue binding, and therefore often is used in place of avidin. Both avidin and streptavidin have a tetravalency for biotin, thus permitting amplification when the former bind to biotin.
In a prior art 2-step procedure, a targeting antibody is conjugated with either avidin or biotin and then is injected into a patient, thus localizing the avidin or biotin at a tumor of interest. Thereafter, either biotin or avidin (depending on which was coupled to the targeting antibody), bearing an imaging isotope is injected and is localized at the site of the primary antibody by binding to avidin or biotin respectively.
Timing of the second injection after the first one is very critical. Injecting the radiolabeled avidin or biotin too early will increase the avidin/biotin conjugates in the bloodstream and nontargeted tissues, while injecting very late may decrease the amount targeted to the tumor because of reduced retention of the primary antibody at the tumor.
Paganelli et al. (Int. J. Cancer 2:121, 1988) and Kalofonos et al. (J. Nucl. Med. 31:1791, 1990) demonstrated the feasibility of the above approach (the former used biotinylated antibody; the latter used streptavidin-conjugated antibody for tumor localization). In work reported by Kalofonos et al. (ibid.), 3 of 10 patients showed improved imaging. However, the patients also showed that labeled biotin alone (without antibody pretargeting) could detect tumors in 8 of 10 patients.
Paganelli et al. (J. Nucl. Med. 31:735, 1990 and Cancer Res. 51:5960, 1991) disclose a 3-step approach wherein a biotinylated antibody is administered, followed by cold, i.e., non-labeled and non-conjugated, avidin to clear nontargeted antibody, and then a radiolabeled biotin is given which binds to the avidin retained in the body, presumably where the avidin has complexed to the biotinylated antibody. By this method, Paganelli et al. were able to show, with the exception of the kidneys, high tumor:normal organ ratios. Therefore, a need exists for better methods and compositions which will allow for higher and more selective targeting and retaining detection and therapeutic agents to and at pathological lesions and for retaining higher amounts of biotin with the original antibody.